1. Field of the Invention
The present invention relates to a pintle injector, and more particularly to a pintle injector with a simple structure and low cost that uniformly atomizes and mixes fuel and oxidizer that can contribute to further improvements in the combustion efficiency of the combustion reaction in a combustion chamber.
2. Description of the Related Art
Liquid rockets have a more complex structure compared with solid rockets. However, they have advantages such as suitability for large scale, thrust can be easily controlled, and so on. Therefore they are widely used in the main propulsion system of rockets for space transportation, or in the gas jet devices for orbiter maneuvering system or reaction control system of artificial satellites.
Liquid rockets are classified according to the propellant into monopropellant propulsion systems and bipropellant propulsion systems. In monopropellant propulsion systems the propellant undergoes a self decomposition reaction aided by a catalyst, and generates high temperature and high pressure combustion gas, and thrust is generated by ejecting the gas from a nozzle. In bipropellant propulsion systems, a fuel is provided for combustion reaction with an oxidizer in a combustion chamber to generate high temperature and high pressure combustion gases, and thrust is generated by ejecting the combustion gas from a nozzle. Generally the thrust F is expressed as the product of the combustion Pc, the area of the nozzle throat A1, and a propulsion coefficient CF determined by the nozzle shape and other factors. Therefore, for both monopropellant and bipropellant propulsion systems, the combustion efficiency in the combustion chamber of either monopropellant or bipropellant rockets is one of the very important factors from the point of view of obtaining the required combustion pressure Pc.
Therefore for bipropellant propulsion systems it is a requirement for injectors that supply propellant to the combustion chamber that fuel and oxidant is atomized, mixed, and burned without the occurrence of combustion vibrations, combustion spikes, localized melting, or other anomalous combustion. Conventionally, the so-called coaxial type injector is known, in which on a injector surface plate many coaxial injector elements are located concentrically, and fuel is injected around and parallel to the oxidant (for example, Japanese Patent Application Laid-open No. 2005-61385).
Also, the so-called impinging type pintle injector is known, in which part of the propellant channel for the fuel or the oxidizer projects into the combustion chamber, and fuel or oxidizer is injected from the pintle, and the fuel and oxidizer stream are made to impinge each other (see for example, U.S. Pat. Nos. 3,699,772, 6,185,927, 6,591,603).
In the coaxial type injector disclosed in Japanese Patent Application Laid-open No. 2005-61385, combustion mainly occurs near the surface of the injector. Therefore combustion of the fuel and oxidizer can occur before the fuel and oxidizer have been uniformly atomized and mixed. This could result in combustion vibrations, combustion spikes, or other abnormal combustion, and lowering of combustion efficiency.
On the other hand, in the pintle injectors disclosed in U.S. Pat. Nos. 3,699,772, 6,185,927, and 6,591,603, part of the propellant channel projects into the combustion chamber, and either the fuel or oxidizer propellant is injected radially, and the other propellant is injected axially. It has the advantages that mixing is improved because the angle of intersection of the fuel stream and the oxidizer stream is about 90° and manufacturing cost can be reduced drastically by the simple structure compared to the coaxial type injectors.
However, in case of using the above pintle injectors the combustion efficiency was reported at best 90˜95%, and the problem is that it is difficult to improve this combustion efficiency to the further level.